Clamping elements in which a workpiece, a tool, a device or a mold is tensioned by means of a piston that can be withdrawn and extended, are known from practice. Likewise, support elements are known from practice, by means of which workpieces that are already tensioned per se are supported to avoid unacceptable deformations at certain points by a piston that can be withdrawn and extended. In machine tools for cutting, in particular, the piston must be sealed in order to prevent cutting oil from penetrating into a housing of the clamping or support element. The cutting oil is often under a high pressure, so that very high requirements are imposed on the seal.
The sealing has hitherto been performed by means of a fixed wiping ring, which keeps away coarse dirt particles, for example, chips. A circular groove, into which a seal is inserted, is recessed into a hole of the wiping ring. This seal, usually an O-ring, ensures the liquid-tight sealing of the piston against the wiping ring. The depth of the groove is selected to be smaller than the diameter of the seal, i.e., for example, of the O-ring. The O-ring is deformed elastically as a result and exerts a normal force on the piston, which ensures tightness. The pressure, which is maintained now at such a level that it ensures sealing, depends on the value of the normal force (pretension of the O-ring) and consequently on the ratio of the groove depth to the O-ring diameter. A low ratio means great deformation of the O-ring and consequently a high normal force (high mechanical pretension of the O-ring) and also great tightness.
It is disadvantageous here that the friction between the piston and the seal also increases proportionally with the normal force because of the coefficient of friction. This may lead to disturbances especially in support elements because of undefined contact forces of the piston against the workpiece.